1. Field of the Invention
The invention relates to a method of sampling in flameless atomic absorption spectrophotometry.
2. Description of the Prior Art
Atomic absorption analysis is a method for the quantitative determination of an element in a sample to be analyzed and is based on measurement of the optical attenuation of a beam of atomic resonance radiation by atoms of the element which are in the ground state.
The known atomic absorption spectral instruments include as an atomizing device an electrically heatable graphite cuvette into which the sample is introduced by way of a sample inlet either by hand or by an automatic pipette. The current flowing through the graphite tube is automatically controlled by a programmable control system, so that the sample, in accordance with a series of time-sequential steps is first dried, then ashed, and finally atomized (vaporized). This procedure of elemental quantitation in the graphite cuvette makes use of a limited amount of sample and vaporizes the sample completely. The dissolved sample must be introduced into the graphite tube in precisely known amount. A time-dependent analytical signal is measured, in which the time-variation of absorption depends on the state of the sample. According to the known prior state of the art, methods and apparatus are known for automatic sampling in flameless atomic absorption spectrophotometry, as described for example in publication No. 1419/3.76 by the company Bodenseewerk Perkin-Elmer, in which programmed control of the automatic analysis sequence permits repeated analyses of a sample having a known elemental content, in order to determine the precision of the measured value.
These prior known arrangements are not completely satisfactory, in that they have the disadvantage, when different sample volumes are to be used, that different settings must be made on the instrument or that the pump module must be changed. Also, the different liquid volumes in the graphite cuvette spread out in varying degree, and upon being atomized contribute in varying amount to the non-specific absorption. Moreover, the reproducibility of the measurements depends upon the sample volume such that relatively small sample volumes, which do not spread out in varying degree, usually provide better reproducibility.